Thomas Savery has grown up in a mining district of Devon and knows the problem of flooded mines. In 1698 he obtains a patent for an engine to raise water 'by the Impellent Force of Fire'. It turns out to be the world's first practical steam engine. Designed purely as a pump, it has no piston but relies on the power of a vacuum.

A metal cylinder is filled with steam from a boiler. Cold water is poured over the outside, condensing the steam within and creating a vacuum which sucks water up through a pipe at the base. When the cylinder is full of water, the valve from below is closed. Steam is again introduced, forcing the water out of the cylinder through another valve. With the cylinder again full of steam, the process is repeated.

In 1702 Savery publishes a book about his invention, entitled The Miner's Friend. In it he describes how the idea came to him. One evening, after finishing his wine, he threw the empty bottle into the fire and prepared to wash his hands in a basin of water. Noticing steam coming out of the neck of the bottle, he plucked it from the fire and stuck it neck down in the basin. As the bottle cooled, it sucked up the water.

The story sounds improbable, and it may be Savery's way of trying to justify his patent - for the principles involved are already well known to contemporary scientists. What the pamphlet does show is that Savery intends to make money from his invention by supplying pumps to mines.

As it turns out, the maximum levels of pressure and vacuum achieved by Savery cannot lift water more than about twelve yards - too little for most mines.

Instead he finds his main customers among progressive country landowners, who are attracted by being at the cutting edge of technology. They use Savery's pumps to raise water for their houses and gardens.

Boiler, cylinder and piston: 1704-1712

Two Devon metalworkers - Thomas Newcomen, a Dartmouth blacksmith, and his assistant John Calley, a glassblower and plumber - are making good progress in some potentially very profitable experiments. They know the high cost of the horse-driven pumps which raise water from the copper and tin mines of Devon and Cornwall. So they are working on a steam pump.

Though probably unaware of this, they are combining two elements pioneered separately by Denis Papin and Thomas Savery - Papin's piston and Savery's separation of the boiler (providing the supply of steam) from the cylinder (where the steam does its work).

In Newcomen's engine the piston, emerging from the top of the cylinder, is attached by an iron chain to one end of a beam which seesaws on a central pivot. At the other end of the beam another chain leads down to the water-pumping mechanism.

Steam released from the boiler into the cylinder pushes up the piston. When the cylinder is full of steam, the same procedure follows as in Savery's engine. Cold water poured on the outside condenses the steam and creates the vacuum. But in this case, instead of directly sucking up water, the vacuum causes the piston to descend in the cylinder. The chain drags down one end of the beam, activating the pump at the other end.

As so often in the advance of science and technology, an accident provides Newcomen with the refinement which brings his pump up to an economic speed. A flaw develops in one of the seams of his cylinder. As a result some cold water, intended only to flow down the outside, gets into the cylinder when it is full of steam. It creates a vacuum so rapid and so powerful that it snaps the chain attaching the piston to the beam.

With this event another lasting feature of the steam engine is discovered. In all Newcomen's developed engines, which soon start work in England's mines, the steam is condensed by a jet of cold water injected into the cylinder.

The first of Newcomen's working engines is installed in 1712 at a colliery near Dudley Castle. It operates successfully here for some thirty years, as the first of many in the mining districts of Britain. Newcomen's machine undoubtedly infringes Savery's patent, for there is no denying that it works 'by the Impellent Force of Fire'. But Savery is having no great commercial success with his own machine. The two men come to an amicable arrangement, the details of which are not known.

Even with Newcomen's improvements, these machines are suitable only for the slow relentless work of pumping in the mines. Proof of the wider potential of the steam engine must await the inventive genius of James Watt.

Mercury thermometer:1714-1742

Gabriel Daniel Fahrenheit, a German glass-blower and instrument-maker working in Holland, is interested in improving the design of thermometer which has been in use for half a century. Known as the Florentine thermometer, because developed in the 1650s in Florence's Accademia del Cimento, this pioneering instrument depends on the expansion and contraction of alcohol within a glass tube.

Alcohol expands rapidly with a rise in temperature, but not at an entirely regular speed of expansion. This makes accurate readings difficult, as also does the sheer technical problem of blowing glass tubes with very narrow and entirely consistent bores.

By 1714 Fahrenheit has made great progress on the technical front, creating two separate alcohol thermometers which agree precisely in their reading of temperature. In that year he hears of the researches of a French physicist, Guillaume Amontons, into the thermal properties of mercury.

Mercury expands less than alcohol (about seven times less for the same rise in temperature), but it does so in a more regular manner. Fahrenheit sees the advantage of this regularity, and he has the glass-making skills to accomodate the smaller rate of expansion. He constructs the first mercury thermometer, of a kind which subsequently becomes standard.

There remains the problem of how to calibrate the thermometer to show degrees of temperature. The only practical method is to choose two temperatures which can be independently established, mark them on the thermometer and divide the intervening length of tube into a number of equal degrees.

In 1701 Newton has proposed the freezing point of water for the bottom of the scale and the temperature of the human body for the top end. Fahrenheit, accustomed to Holland's cold winters, wants to include temperatures below the freezing point of water. He therefore accepts blood temperature for the top of his scale but adopts the freezing point of salt water for the lower extreme.

Measurement is conventionally done in multiples of 2, 3 and 4, so Fahrenheit splits his scale into 12 sections, each of them divided into 8 equal parts. This gives him a total of 96 degrees, zero being the freezing point of brine and 96° (in his somewhat inaccurate reading) the average temperature of human blood. With his thermometer calibrated on these two points, Fahrenheit can take a reading for the freezing point (32°) and boiling point (212°) of water.

A more logical Swede, Anders Celsius, proposes in 1742 an early example of decimilization. His centigrade scale takes the freezing and boiling temperatures of water as 0° and 100°. In English-speaking countries this less complicated system takes more than two centuries to prevail.

Chronometer: 1714-1766

Two centuries of ocean travel, since the first European voyages of discovery, have made it increasingly important for ships' captains - whether on naval or merchant business - to be able to calculate their position accurately in any of the world's seas. With the help of the simple and ancient astrolabe, the stars will reveal latitude. But on a revolving planet, longitude is harder. You need to know what time it is, before you can discover what place it is.

The importance of this is made evident when the British government, in 1714, sets up a Board of Longitude and offers a massive £20,000 prize to any inventor who can produce a clock capable of keeping accurate time at sea.

The terms are demanding. To win the prize a chronometer (a solemnly scientific term for a clock, first used in a document of this year) must be sufficiently accurate to calculate longitude within thirty nautical miles at the end of a journey to the West Indies. This means that in rough seas, damp salty conditions and sudden changes of temperature the instrument must lose or gain not more than three seconds a day - a level of accuracy unmatched at this time by the best clocks in the calmest London drawing rooms.

The challenge appeals to John Harrison, at the time of the announcement a 21-year-old Lincolnshire carpenter with an interest in clocks. It is nearly sixty years before he wins the money. Luckily he lives long enough to collect it.

By 1735 Harrison has built the first chronometer which he believes approaches the necessary standard. Over the next quarter-century he replaces it with three improved models before formally undergoing the government's test. His innovations include bearings which reduce friction, weighted balances interconnected by coiled springs to minimize the effects of movement, and the use of two metals in the balance spring to cope with expansion and contraction caused by changes of temperature.

Harrison's first 'sea clock', in 1735, weighs 72 pounds and is 3 feet in all dimensions. His fourth, in 1759, is more like a watch - circular and 5 inches in diameter. It is this machine which undergoes the sea trials.

Harrison is now sixty-seven, so his son takes the chronometer on its test journey to Jamaica in 1761. It is five seconds slow at the end of the voyage. The government argues that this may be a fluke and offers Harrison only £2500. After further trials, and the successful building of a Harrison chronometer by another craftsman (at the huge cost of £450), the inventor is finally paid the full prize money in 1773.

He has proved in 1761 what is possible, but his chronometer is an elaborate and expensive way of achieving the purpose. It is in France, where a large prize is also on offer from the Académie des Sciences, that the practical chronometer of the future is developed.

The French trial, open to all comers, takes place in 1766 on a voyage from Le Havre in a specially commissioned yacht, the Aurore. The only chronometer ready for the test is designed by Pierre Le Roy. At the end of forty-six days, his machine is accurate to within eight seconds.

Le Roy's timepiece is larger than Harrison's final model, but it is very much easier to construct. It provides the pattern of the future. With further modifications from various sources over the next two decades, the marine chronometer in its lasting form emerges before the end of the 18th century. Using it in combination with the sextant, explorers travelling the world's oceans can now bring back accurate information of immense value to the makers of maps and charts.

Sextant: 1731-1757

The 18th-century search for a way of discovering longitude is accompanied by refinements in the ancient method of establishing latitude. This has been possible since the 2nd century BC by means of the astrolabe. From the beginning of the European voyages in the 15th century practical improvements have been made to the astrolabe - mainly by providing more convenient calibrated arcs on which the user can read the number of degrees of the sun or a star above the horizon.

The size of these arcs is defined in relation to the full circle. A quadrant (a quarter of the circle) shows 90°, a sextant 60° and an octant 45°.

The use of such arcs in conjunction with the traditional astrolabe is evident from a text of 1555 about voyaging to the West Indies. The author talks of 'quadrant and astrolabe, instruments of astronomy'.

The important development during the 18th century is the application of optical devices (mirrors and lenses) to the task of working out angles above the horizon. Slightly differing solutions, by instrument makers in Europe and America, compete during the early decades of the century. The one which prevails - largely because it is more convenient at sea - is designed as an octant in 1731 by John Hadley, an established English maker of reflecting telescopes.

Hadley's instrument, like others designed by his contemporary rivals, uses mirrors to bring any two points into alignment in the observer's sight-line. For the navigator these two points will usually be the sun and the horizon. To read the angle of the sun, the observer looks through the octant's eyepiece at the horizon and then turns an adjusting knob until the reflected orb of the sun (through a darkened glass) is brought down to the same level.

The double reflection means that the actual angle of the sun above the horizon is twice that on the octant's arc of 45%. So Hadley's instrument can read angles up to 90%.

In 1734 Hadley adds an improvement which becomes standard, installing a spirit level so that the horizontal can be found even if the horizon is not visible. In 1757, after Hadley's death, a naval captain proposes that the arc in the instrument be extended from 45° to 60°, making possible a reading up to 120°.

With this Hadley's octant becomes a sextant, and the instrument in use ever since finds its essential form.

The Leyden jar: 1745-1746

The researches of William Gilbert, at the start of the 17th century, lead eventually to simple machines with which enthusiasts can generate an electric charge by means of friction. The current generated will give a stimulating frisson to a lady's hand, or can be discharged as a spark.

In 1745 an amateur scientist, Ewald Georg von Kleist, dean of the cathedral in Kamien, makes an interesting discovery. After partly filling a glass jar with water, and pushing a metal rod through a cork stopper until it reaches the water, he attaches the end of the nail to his friction machine.

After a suitable amount of whirring, the friction machine is disconnected. When Kleist touches the top of the nail he can feel a slight shock, proving that static electricity has remained in the jar. It is the first time that electricity has been stored in this way, for future discharge, in the type of device known as a capacitor.

In 1746 the same principle is discovered by Pieter van Musschenbroek, a physicist in the university of Leyden. As a professional, he makes much use of the new device in laboratory experiments. Though sometimes called a Kleistian jar, it becomes more commonly known as the Leyden jar.

James Watt and the condenser: 1764-1769

In 1764 a model of a Newcomen steam engine is brought for repair to the young James Watt, who is responsible for looking after the instruments in the physics department of the university of Glasgow. In restoring it to working order, he is astonished at how much steam it uses and wastes.

The reason, he realizes, is that the machine's single cylinder is required to perform two opposing functions. It must receive the incoming steam at maximum pressure to force the piston up (for which it needs to be as hot as possible), and it must then condense the steam to form a vacuum to pull the cylinder down (for which it needs to be as cool as possible).

The solution occurs to Watt when he is walking near Glasgow one Sunday in May 1765. The two functions could be separated by providing a chamber, outside the cylinder but connecting with it, in which a jet of cold water will condense the steam and cause the vacuum.

This chamber is the condenser, for which Watt registers a patent in 1769. The principle has remained an essential part of all subsequent steam engines. It is the first of three major improvements which Watt makes in the basic design of steam-driven machinery. The other two are the double-acting engine and the governor, developed in the 1780s.

Machine tools, gun barrels and cylinders: 1774-1800

John Wilkinson, an ironmaster in Staffordshire and Shropshire, has been building up a lucrative arms trade. In 1774 he invents a machine, powered by a water wheel, which can drill with unprecedented accuracy through the length of a cast-iron cylinder to create the barrel of a cannon. It is a turning point in the development of machine tools.

James Watt realizes that Wilkinson's new machine is capable of the precision required for an efficient steam-engine cylinder. In 1775 Wilkinson delivers to Birmingham the first of the thousands of cylinders he will bore for the firm of Boulton and Watt. Boulton finds them 'almost without error; that of 50 inches diameter doth not err the thickness of an old shilling' in any part.

Double-acting engine and governor: 1782-1787

Just as James Watt applied a rational approach to improve the efficiency of the steam engine with the condenser, so now he takes a logical step forward in a modification patented in 1782. His new improvement is the double-acting engine.

Watt observes that the steam is idle for half of each cycle. During the downward stroke, when the vacuum is exerting atmospheric force on the piston, the valve between boiler and cylinder is closed. Watt takes the simple step of diverting the steam during this part of the cycle to the upper part of the cylinder, where it joins with the atmospheric pressure in forcing the cylinder down - and thus doubles its effective action.

The most elegant contraption devised by Watt is in use from 1787. It is the governor - the first example of the type of controlling device required in industrial automation, and a feature of all steam engines since Watt's time.

Watt's governor consists of two arms, hinged on a central pivot and rotated by the action of the steam engine. Each arm has a heavy ball at the end. As the speed increases, centrifugal force moves the balls and the arms outwards. This action narrows the aperture of a valve controlling the flow of steam to the engine. As the power is slowly cut off, the speed of the engine reduces and the balls subside nearer to the central column - thus slightly opening the valve again in a permanent process of adjustment.

Year of the balloon - hot air:1783

Although hydrogen has been isolated by Cavendish in the 1760s, and shown to be fourteen times lighter than air, it is not until the early 1780s that Europe's inventors are suddenly gripped with a feverish interest in using the concept to achieve a form of flight. In 1781-2 scientists in both England and Switzerland fill soap bubbles with hydrogen and see them rise rapidly to the ceiling, but similar experiments with animal bladders prove disappointing.

In the event a more elementary idea, requiring none of the achievements of recent researches, provides the breakthrough.

In November 1782 a French manufacturer of paper, Joseph Montgolfier, wonders whether the simple fact of smoke rising might not be used to carry a balloon aloft. With his brother Etienne he begins making experiments. By June 1783 they are sufficiently confident to give a public demonstration in the town of Annonay.

They light a bonfire of straw and wool under a canvas and paper balloon with a diameter of about 35 feet. An astonished crowd sees the apparatus inflate and then drift into the sky. It rises, they estimate, to more than 3000 feet, stays in the air for ten minutes, and descends gently to earth 1500 yards away.

A report is immediately sent by the representatives of the local assembly to the Academy of Sciences in Paris. The news causes a sensation. The Montgolfiers are invited to the capital to demonstrate their invention.

Etienne makes the journey on their joint behalf and constructs a balloon to be launched at Versailles on September 19 in the presence of Louis XVI. This time the flying globe or aerostatic sphere (both are contemporary phrases) carries living passengers - a sheep, a cock and a duck. The trio travel more than two miles and land unharmed, except that the cock has been kicked by the sheep. The king, watching it all through his telescope, raises the Montgolfier family into the ranks of the nobility.

The final Montgolfier triumph takes place in November. A larger balloon is constructed, 46 feet in diameter, with a metal container (to hold the burning straw) hanging on chains just inside it. A basket, suspended below, is large enough to carry two people. Rigorous tests take place in a Paris garden. The tethered balloon, now bearing a passenger (Pilâtre de Rozier), is allowed to rise to successively greater heights.

At last, on November 21, all is considered ready. Four hands will be needed to stoke the fire with bundles of straw. Pilâtre is joined by a fellow passenger, the marquis d'Arlandes.

An excited crowd attempts to follow the path of the balloon as it rises and drifts away across Paris. In spite of alarming moments (such as their basket catching fire), the aeronauts make a successful flight, travelling about six miles in twenty-five minutes. They land safely, narrowly missing a windmill.

Those who have followed on horses are immediately on the scene. In the excitement Pilâtre's jacket, which he has taken off in the heat of the work, is torn to shreds and distributed as souvenirs. History has its first aviators.

Year of the balloon - hydrogen: 1783

News of the astonishing event at Annonay, in June 1783, prompts a Parisian physicist, Jacques Alexandre César Charles, to take serious steps to harness the property of hydrogen. He commissions from a silk merchant a balloon with a diameter of about 13 feet, and has it varnished with a gum solution.

To provide enough hydrogen Charles acquires 500 lb. of sulphuric acid and 1000 lb. of iron filings. The resulting gas is passed for four days through lead pipes into the slowly inflating balloon. At last, on August 27, a cannon is fired to signal the launch. The balloon rises rapidly to about 3000 feet in front of an ecstatic crowd on the Champ de Mars.

The contraption travels fifteen miles in forty-five minutes before springing a leak and crashing to the ground near a village. The first peasants on the scene, alarmed at the arrival of this monster from the sky, take the precaution of beating it until it seems undeniably dead.

Just as the hydrogen balloon is behind the hot-air version in the first ascent of any kind, so it is in the first manned ascent - but only by a very small margin. On December 1, ten days after the achievement of Pilâtre de Rozier, Charles and a colleague rise into the air from the circular pond in front of the Tuileries. After a trouble-free journey of more than two hours, the aeronauts land about twenty-seven miles from Paris.

Charles's balloon, as befits that of a scientist, is more controllable than the Montgolfier version. It has a valve to release gas and descend, and it carries ballast which can be thrown overboard to rise again. The basket to carry the aeronauts is now a sturdy construction, looking like a small ship or gondola. And there is a barometer on board to measure altitude.

After the first landing, Charles takes off alone for a second flight. The barometer reveals that with the lighter load the balloon reaches the impressive height of about 10,000 feet, or two miles.

The hydrogen balloon soon prevails over the hot-air variety, because of its greater sophistication in an age when heat depends on burning bales of straw. Magnificent feats are achieved, beginning with a flight in 1785 across the English Channel by Jean Pierre Blanchard and an American doctor, John Jeffries. They throw out every loose item in the gondola, including their own clothes, to stay aloft long enough to arrive naked in France.

Impressive though these adventures are, the basic problem remains that there is no way of guiding a balloon.

Bifocals: 1784

As he advances in years, Benjamin Franklin needs two pairs of spectacles - one for reading and one for distance. Like everyone else, he finds changing his spectacles tiresome. The other pair is invariably mislaid when needed.

At the age of seventy-eight this most practical of scientists finds the obvious solution. He commissions from his spectacle-maker semicircular lenses of each variety and a frame which will hold a pair of these semicircles tightly together for each eye - the concave half at the top for the distance, the convex at the bottom for reading. The bifocal lens is born.

Cotton gin: 1793

The mechanization of spinning and weaving in England, between 1733 and 1785, greatly speeds up the industrial process and rapidly leads to a shortage of cotton. During most of the century the bulk of raw cotton arriving at Liverpool for the Lancashire mills is from India. The cotton grown in the southern states of America is commercially less viable because it is short-fibred.

The cotton fibres, which will be spun into cotton, have to be separated from the seeds which they protect and enmesh. This process, known as cotton picking, is done entirely by hand. The short fibres make it a slow and expensive task.

In 1793 Eli Whitney, a graduate of Yale, invents a machine which solves this problem. It consists of a hand-turned roller with projecting spikes. Each spike passes through a slot in a grid, wide enough to allow the spike to drag the cotton fibres through but too narrow for the cotton seeds to pass. They fall out into a separate container, while a revolving brush cleans the fibres, or lint, off the spikes.

Whitney's machine immediately trebles the speed at which cotton can be ginned, with major effects on the economy of the southern states of America. About forty times as much cotton (now established as 'king cotton') is produced in 1810 as in 1793. Vast new areas are taken in hand as plantations. The demand for slaves increases accordingly.

Lithography: 1798-1875

In 1798 an unsuccessful dramatist, Alois Senefelder, makes a discovery of profound significance in the history of artists' prints and later of commercial printing too. He has been attempting for some while to print from stone (prompted by a famous incident of 1796 when he jots down his mother's laundry list in greasy ink on a slab of limestone). What he comes to realize, in 1798, is that the antipathy between grease and water, familiar in any kitchen, can be used as a basis for printing.

In lithography marks are made on a stone surface in greasy crayon or ink. The stone is then wetted. Newly applied ink will stick only to the greasy marks. Paper pressed against the stone will pick up those marks and nothing else.

Jenner and vaccination: 1796-1798

Working as a country doctor in the Gloucestershire village of Berkeley, Edward Jenner is aware of a local theory that people who have suffered a mild form of pox - caught from the infected udders of cows - never catch the much more dangerous smallpox.

Cowpox is a relatively rare disease, unrecognized at the time by the medical profession, and it is not until 1796 that Jenner has an opportunity to test this theory of immunity. In that year a dairymaid develops the symptoms. Jenner takes material from an eruption on her hand and (using a thorn) inoculates an 8-year-old boy, James Phipps, with the substance. Phipps develops cowpox and soon recovers.

The principle of inoculation has become well established since the efforts of Lady Mary Wortley Montagu to encourage the use of infected matter from smallpox victims as a preventive measure. Six weeks after the cowpox inoculation, Jenner gives James Phipps a conventional smallpox inoculation. The expectation would be that he develops a mild attack of smallpox, survives it and becomes immune. In the event, as Jenner hopes, Phipps shows no sign at all of being infected by the smallpox virus.

Continuing his experiments, Jenner proves that even in a long line of inoculation (taking new vaccine from each successive patient suffering from cowpox) the procedure still confers immunity.

Jenner publishes his findings in 1798 in the splendidly titled An Inquiry into the Causes and Effects of the Variolae Vaccinae, a disease discovered in some of the Western Counties of England, particularly Gloucestershire, and known by the name of Cow Pox.

Variolae Vaccinae, meaning literally 'smallpox of cows', is Jenner's scholarly name for cowpox. The phrase soon provides the word vaccination (initially coined in France as a term of mockery) for this new form of inoculation against smallpox. After some initial opposition from the medical establishment, vaccination proves its merits and the use of it rapidly spreads. As early as 1807 it is made compulsory in Bavaria (though not till 1853 in Britain).

In 1806 the president of the USA, Thomas Jefferson, writes to Jenner: 'Future generations will know by history only that the loathsome smallpox existed and by you has been extirpated.' He is right, but the process takes longer than the president probably expects - even though the immediate effects are impressive. In Britain the annual death rate from smallpox falls during the 19th century from about 2000 per million to well under 100. But diseases are difficult to extirpate on a worldwide basis.

Nevertheless smallpox is the first disease with which that aim is eventually achieved. After intensive international vaccination programmes, there is by 1980 no case of smallpox on the planet.

Percussion: from1807

Alexander Forsyth, a Scottish clergyman who enjoys shooting wildfowl, finds that the flash from his flintlock often alerts the sitting ducks which are his target. Sometimes they even fly away or dive before his ball reaches them.

Searching for a priming substance which will ignite without a spark, he discovers that potassium chlorate will do the job if struck a sharp blow. He successfully builds himself a fowling piece which fires by percussion. When his gun comes to the attention of the military, he is installed in the Tower of London to continue his experiments. By 1807 he has shown that his powder will work in any size of musket or cannon. His discovery is a turning point in the story of gunfire.